To believers such as Larry Burns, General Motors' vice president of research and development, the frenzy is validation — maybe even vindication — that hydrogen is quickly gaining acceptance as the eventual replacement for gasoline. "I think we're beginning to reach a tipping point," he said, standing next to the Sequel hydrogen concept vehicle introduced in January in Detroit. "Our industry is very serious."

Some automakers are in a hurry. Mazda announced that it will begin production of a hydrogen version of its sporty RX-8 within three years, starting in Japan. Instead of more complicated fuel-cell stacks that produce energy through a chemical reaction, Mazda's solution is to burn hydrogen in the car's rotary engine. Hydrogen combustion results in some emissions but far fewer than from a gasoline-only engine.

The RX-8 Hydrogen RE is also being called a hybrid because if it runs out of its store of hydrogen, it can switch to a separate gasoline tank.

Japan has about 15 hydrogen fueling stations, 10 around Tokyo. By the time the car goes on sale, most likely to government and corporate fleets at first, the number of fueling stations is likely to be about 30, says Mazda engineer Akihiro Kashiwagi.

Hydrogen's popularity at the show, which continues through Nov. 6, is recognition of the potent selling power of environmentalism. But the molecule's attraction is also stoked by soaring gasoline prices and fears related to global warming.

Most experts have held that the switch to hydrogen likely won't come for 15 to 20 years because of the need to not only design and build the cars but to figure out ways to make the fuel and to build fueling stations. Ron Cogan of Green Car Journal, refers to "the chicken, the egg and the coupe problem. Without infrastructure, nobody develops vehicles; without vehicles, nobody develops infrastructure."

But he and others say solutions could come sooner rather than later. "Serious production" of hydrogen cars will begin in the next seven to 10 years, predicts Andreas Docter, senior manager of DaimlerChrysler's fuel-cell systems engineering.